CVE-2026-57575 in Misskey
Summary
by MITRE • 07/10/2026
Misskey is an open source, federated social media platform. Prior to 2026.6.0, Misskey contains a Server-Side Request Forgery (SSRF) vulnerability in URL preview functionality in UrlPreviewService. Due to missing network restrictions before establishing outbound connections, a remote attacker can cause the Misskey server to initiate HTTP requests to loopback, private, or link-local services. Because IP address validation takes place after the request has been sent and the process is subsequently rejected, no sensitive internal data is believed to be transmitted back or exposed to the attacker. This issue is fixed in version 2026.6.0.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 07/10/2026
The Misskey federated social media platform experienced a critical Server-Side Request Forgery vulnerability in its URL preview functionality prior to version 2026.6.0. This vulnerability resides within the UrlPreviewService component which handles automatic preview generation for external links shared on the platform. The flaw represents a classic SSRF weakness that allows remote attackers to manipulate the application's outbound network requests through crafted input data. The vulnerability stems from inadequate network access controls and validation mechanisms that permit arbitrary destination addresses to be requested before proper security checks are performed.
The technical implementation of this vulnerability demonstrates a fundamental flaw in the request processing flow where network restrictions are bypassed during the initial connection establishment phase. Attackers can exploit this by crafting malicious URLs that, when processed by the UrlPreviewService, cause the Misskey server to initiate HTTP requests to internal network addresses including loopback interfaces, private IP ranges, and link-local addresses. This behavior violates standard security principles for outbound request handling and creates opportunities for internal network reconnaissance and potential lateral movement within compromised environments. The vulnerability classification aligns with CWE-918 which specifically addresses Server-Side Request Forgery vulnerabilities.
The operational impact of this SSRF vulnerability extends beyond simple network reconnaissance as it could potentially enable attackers to map internal network topologies, identify running services on private networks, and discover sensitive internal systems that might otherwise remain hidden from external view. While the specific implementation prevents data exfiltration since validation occurs after request initiation and subsequent rejection of invalid connections, the attack surface remains significant for information gathering purposes. This vulnerability particularly affects federated platforms like Misskey where user-generated content is processed and previewed, creating numerous potential attack vectors through shared links and media content.
Security mitigations for this vulnerability include implementing strict network access controls that prevent outbound requests to internal address ranges before connection establishment occurs. The fix implemented in version 2026.6.0 addresses the core issue by enforcing proper validation mechanisms that reject connections to loopback, private, and link-local addresses prior to initiating outbound requests. This approach follows ATT&CK technique T1566 which emphasizes the importance of network boundary controls and request validation. Organizations using Misskey should implement additional protective measures including network segmentation, outbound proxy configurations, and regular security assessments to prevent similar vulnerabilities in other components of their federated social media infrastructure. The vulnerability serves as a reminder of the critical importance of proper input validation and network access control enforcement in applications that process external content and generate previews for user consumption.